fix(proxy): treat omitted auth on config pass-through routes as enforced at registration (rc/1.104.0 backport of #44253)

[yuneng-berri]

TLDR

Problem this solves:

• Failed requests on config pass-through routes without auth are missing from spend logs
• Regression from fix(proxy): restore pre-config-wins handling of pass-through endpoints #43962, which reached rc/1.104.0

How it solves it:

• Backport of fix(proxy): treat omitted auth on config pass-through routes as enforced at registration #44253: omitted auth registers as enforced, matching request-time auth
• Clean cherry-pick of its three commits, no adaptation needed

Depends on #44253 landing on main first

User Flow

Before: an admin's config pass-through route with no auth key hides upstream failures from spend logs

1. The admin adds /audit-pt to general_settings.pass_through_endpoints with include_subpath: true and no auth
2. A developer sends POST https://litellm-domain/audit-pt with a valid virtual key
3. The upstream rejects it and the developer gets back a 403 with the upstream error body
4. The admin queries GET https://litellm-domain/spend/logs and finds no row for that request

After: the same failed request shows up in spend logs as a failure row

1. Same config, no auth key
2. Same POST https://litellm-domain/audit-pt with a valid virtual key
3. Same 403 with the upstream error body
4. GET https://litellm-domain/spend/logs now returns a failure row for that request id with error code 403

Relevant issues

Backport of #44253 to rc/1.104.0. Regression from #43962

Affected release

#43962 reached rc/1.104.0 through #44054 after v1.104.0-rc.2, so no tagged 1.104 build has the regression yet. This keeps it out of the next rc

Pre-Submission checklist

Please complete all items before asking a LiteLLM maintainer to review your PR

• I have added meaningful tests
• The handful of test files covering my change pass locally, e.g. uv run pytest tests/test_litellm/<your_test_file>.py -v. Leave the suites (make test-unit-*, make test-unit) to CI: it finishes in ~15 minutes where a laptop takes an hour or more
• My PR passes all required CI/CD checks (e.g., lint, schema.d.ts sync check, etc.)
• My PR's scope is as isolated as possible; it only solves 1 specific problem
• I have received a Greptile Confidence Score of at least 4/5 before requesting a maintainer review (Greptile reviews automatically once the PR is opened; only comment @greptileai to re-request a review after pushing changes)

Delays in PR merge?

If you're seeing a delay in your PR being merged, ping the LiteLLM Team on Slack (#pr-review).

Screenshots / Proof of Fix

Live proxy with a real Postgres and a local upstream that always answers 403 {"error": {"message": "max budget reached for this deployment"}}, same config on both sides. MK is the master key and KEY the virtual key from step 1. The After tip 1cca114193 only adds a test formatting commit on top of 95a14d70a3, so the production code is identical

model_list: []
general_settings:
  master_key: os.environ/LITELLM_MASTER_KEY
  database_url: os.environ/DATABASE_URL
  proxy_batch_write_at: 1
  pass_through_endpoints:
    - path: /audit-pt
      target: http://127.0.0.1:8291/upstream
      include_subpath: true

The regression unit test test_pass_through_registration_auth_enforcement fails its two config-omitted cases on rc/1.104.0 and passes with this PR

Before (2e5981c)

1. Create a virtual key

$ curl -s -X POST localhost:4721/key/generate -H "Authorization: Bearer $MK" -H 'Content-Type: application/json' -d '{"key_alias": "audit-proof"}' | jq -r .key
sk-...clFg

2. Call the config route with that key, the upstream answers 403

$ curl -s -i -X POST localhost:4721/audit-pt -H "Authorization: Bearer $KEY" -H 'Content-Type: application/json' -d '{"contents":[{"parts":[{"text":"hi"}]}]}' | grep -iE '^HTTP|^x-litellm-call-id|^\{'
HTTP/1.1 403 Forbidden
x-litellm-call-id: 537e52eb-079c-460d-8b1b-1983d77c4b2c
{"error": {"message": "max budget reached for this deployment"}}

3. Read spend logs for pass-through rows

$ curl -s 'localhost:4721/spend/logs?start_date=2026-01-01&end_date=2027-01-01&summarize=false' -H "Authorization: Bearer $MK" | jq '[.[] | select(.call_type=="pass_through_endpoint") | {request_id, status, call_type, api_key_alias: .metadata.user_api_key_alias, error_code: .metadata.error_information.error_code}]'
[]

After (95a14d7)

1. Create a virtual key

$ curl -s -X POST localhost:4722/key/generate -H "Authorization: Bearer $MK" -H 'Content-Type: application/json' -d '{"key_alias": "audit-proof"}' | jq -r .key
sk-...mnJw

2. Call the config route with that key, the upstream answers 403

$ curl -s -i -X POST localhost:4722/audit-pt -H "Authorization: Bearer $KEY" -H 'Content-Type: application/json' -d '{"contents":[{"parts":[{"text":"hi"}]}]}' | grep -iE '^HTTP|^x-litellm-call-id|^\{'
HTTP/1.1 403 Forbidden
x-litellm-call-id: 3e7e6a73-56a7-4c1f-8c10-f859348560e0
{"error": {"message": "max budget reached for this deployment"}}

3. Read spend logs for pass-through rows

$ curl -s 'localhost:4722/spend/logs?start_date=2026-01-01&end_date=2027-01-01&summarize=false' -H "Authorization: Bearer $MK" | jq '[.[] | select(.call_type=="pass_through_endpoint") | {request_id, status, call_type, api_key_alias: .metadata.user_api_key_alias, error_code: .metadata.error_information.error_code}]'
[
  {
    "request_id": "3e7e6a73-56a7-4c1f-8c10-f859348560e0",
    "status": "failure",
    "call_type": "pass_through_endpoint",
    "api_key_alias": "audit-proof",
    "error_code": "403"
  }
]

Type

🐛 Bug Fix
✅ Test

Caveats (if any)

Severe

• Config routes without auth get the same key checks as auth: true again
  • Non-admin keys need allowed_passthrough_routes on subpaths
  • Keys limited to allowed_routes: ["llm_api_routes"] now get 403
  • Over-budget keys get 422 on these routes
  • Matches behavior before fix(proxy): restore pre-config-wins handling of pass-through endpoints #43962 on proxies with a database
• Proxies without a database now enforce this too, which they never did
  • Set auth: false on the entry to keep the old behavior

Low

• The integration node test_config_pass_through_route_logs_body_and_strips_query was not run on this line, the live run above covers the same path

[greptile-apps]

Confidence Score: 5/5

[Critical risk] Changes default authentication enforcement for proxy pass-through routes.

The PR appears safe to merge; no actionable defects were found

What we checked:

• Upstream model names stay untouched: The proxy recognizes the dispatched pass-through handler and skips model extraction and alias rewriting
• Tests remove their registered routes: Each case cleans up in finally; the cleanup removes the exact path, wildcard path, and registry entries

Summary

Config pass-through routes now register omitted auth as True, matching the existing request-time default. This makes their upstream failures eligible for spend logs

• Added eight cases covering config and database defaults, explicit auth: false, exact paths, and subpaths
• No actionable defects or rule violations found
• Tests were inspected, not run

Acknowledged behavior changes: yuneng-berri explicitly states that omitted-auth routes gain route-grant and budget checks, and that proxies without a database now enforce authentication. These changes are intentional; auth: false preserves the old behavior

_{Reviews (1) · Last reviewed commit: "test(proxy): wrap long pass-through auth..."}

[yuneng-berri]

Closing with #44253: no product change needed, the red test is fixed test-side in #44265 instead.